Women who are obese and who have been metabolically healthy for decades – e.g., they don’t have elevated cholesterol, blood pressure or blood sugar – are still at higher risk of developing cardiovascular disease compared to metabolically healthy women of normal weight. This was the finding from a study that followed over 90,000 American women for up to 30 years.
This suggests that obesity is a risk factor for cardiovascular disease, regardless of whether or not women develop any of the common metabolic diseases such as high blood pressure or type 2 diabetes.
The study also found that the majority of metabolically healthy women are likely to become metabolically unhealthy over time, even if they were normal weight.
Obesity (having a BMI of 30 or greater) affects almost all of the cardiovascular disease risk factors, particularly those related to metabolic syndrome including high blood pressure, poor blood sugar control or diabetes and abnormal blood fats, which double the risk of cardiovascular disease such as heart attack and stroke.
However, some people with obesity seem to be free of these risk factors; estimates suggest as many as a third of obese people might be metabolically healthy.
Whether this so-called 'metabolically healthy obesity' is associated with a higher risk of cardiovascular disease has been debated for many years.
About the study
To investigate this further, the researchers examined the connection between obesity and cardiovascular disease in 90,257 women (initially free from cardiovascular disease) from the Nurses' Health Study -- a study tracking the health of female nurses (aged 30-55 years) in the US since 1976.
Participants were divided into groups by weight category, metabolic health (defined as the absence of three metabolic risk factors -- type 2 diabetes, high blood pressure, and high blood cholesterol), and change in metabolic health status, and followed them for up to 30 years. They were sent questionnaires every two years to update their weight and metabolic health status, as well as to assess their lifestyle, health behaviour, and medical history.
The researchers adjusted for a range of factors that may have influenced the results including age, diet, smoking status, physical activity, alcohol consumption, ethnicity or race, highest education level, menopausal status, aspirin use, and family history of heart attack or diabetes.
Cardiovascular disease risk was especially high in all metabolically unhealthy women, regardless of their BMI. Metabolically unhealthy normal-weight women were around 2.5 times more likely to develop cardiovascular disease compared to normal-weight women with no metabolic abnormalities.
Even women with 'metabolically healthy obesity' were at higher risk of cardiovascular disease (39% higher risk).
Furthermore, obese women who maintained metabolic health over 20 years still had a 57% higher risk of developing cardiovascular disease compared to normal-weight metabolically healthy women.
Importantly, most women who were initially metabolically healthy obese (84%), and around two-thirds (68%) of normal-weight metabolically healthy women, became unhealthy over a 20-year period.
The findings highlight the importance of preventing the development of metabolic diseases, and suggest that even people in good metabolic health can benefit from education to improve their diet and increase physical activity to guard against progressing to poor metabolic health.
The authors acknowledge that their findings are correlational rather than cause and effect. However, study strengths include the large number of participants, repeated measurements and the long follow up time.
Source: The Lancet Diabetes & Endocrinology, May 30, 2018.
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